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Abstract:

A device for measuring refractive index of medium based on optical delay
technology comprises: a signal processing and controlling module, an
optical transmitter module, and an optical receiver module, wherein the
signal processing and controlling module controls the optical transmitter
module to transmit an optical signal having a certain wavelength; the
optical signal is injected into a medium to be measured; the optical
signal is transmitted and delayed by the medium; the optical receiver
module receives the optical signal delayed, and transforms the optical
signal delayed into a electrical signal; the electrical signal is
amplified and transmitted to the signal processing and controlling
module; the signal processing and controlling module measures a delay
time between transmitting and receiving the optical signal; and the
refractive index of the medium at the certain wavelength is calculated
based on the delay time and a known length of the medium.

Claims:

1. A device for measuring refractive index of medium based on optical
delay technology, comprising: a signal processing and controlling module,
an optical transmitter module, and an optical receiver module; wherein
the signal processing and controlling module controls the optical
transmitter module to transmit an optical signal having a certain
wavelength; the optical signal is injected into a medium to be measured;
the optical signal is transmitted in the medium to be measured and
delayed by the medium to be measured; after the optical signal delayed
arrives at the optical receiver module, the optical receiver module
transforms the optical signal delayed into a electrical signal, and the
electrical signal is amplified and transmitted to the signal processing
and controlling module by the optical receiver module; the signal
processing and controlling module measures a delay time between
transmitting the optical signal and receiving the optical signal; and a
refractive index of the medium to be measured at the certain wavelength
is calculated according to the delay time and a known length of the
medium to be measured.

2. The device for measuring refractive index of medium based on optical
delay technology, as recited in claim 1, wherein the optical transmitter
module is a semiconductor laser or a solid laser, transmitting the
optical signal having the certain wavelength; and after direct intensity
modulation or indirect intensity modulation, the optical transmitter
module transmits an optical signal in a shape of continuous sine or
pulse.

3. The device for measuring refractive index of medium based on optical
delay technology, as recited in claim 1, wherein the optical receiver
module is a PIN photoelectric detector or an APD photoelectric detector,
which detects the optical signal transmitted and delayed by the medium to
be measured; and the optical receiver module has a working wavelength
matching with the optical transmitter module.

4. The device for measuring refractive index of medium based on optical
delay technology, as recited in claim 1, wherein the medium to be
measured is a medium through which said optical signal is able to pass.

5. The device for measuring refractive index of medium based on optical
delay technology, as recited in claim 3, wherein the medium to be
measured is a medium through which said optical signal is able to pass.

6. A measuring method with the device for measuring refractive index of
medium based on optical delay technology, as recited in claim 1,
comprising steps of: (1) measuring a first delay time of an etalon, i.e.,
t1, with the device for measuring refractive index of medium based
on optical delay technology, wherein a refractive index and a length of
the etalon are respectively known as n1 and L1; (2) replacing
the etalon with a medium to be measured, and measuring a second delay
time t2 with other factors unchanged, wherein a refractive index and
a length of the medium to be measured are respectively denoted as n2
and L2; (3) calculating an additional delay time of an optical
signal with Δt=t1-t2, wherein the additional delay time
is caused by the medium to be measured; and (4) calculating the
refractive index n2 of the medium to be measured with a formula,
i.e., Δt=(n1L1n2L2)/c, wherein
n2=(n1L1-cΔt)/L.sub.2.

7. The device for measuring refractive index of medium based on optical
delay technology, as recited in claim 6, wherein the etalon is a medium
having the known refractive index and the length, air or vacuum.

Description:

BACKGROUND OF THE PRESENT INVENTION

[0001] 1. Field of Invention

[0002] The present invention relates to a field of optoelectronic
technology, and more particularly to a device for measuring refractive
index of medium based on optical delay technology and its method.

[0003] 2. Description of Related Arts

[0004] Methods for measuring refractive index of medium can be divided in
two types, i.e., the transmission type and the reflection type.

[0005] In the transmission-type method, the refractive index of medium to
be measured is calculated based on the characteristic of the transmitted
light which has passed through the medium to be measured. The
transmission-type method mainly comprises: measuring the angle of
incidence of the incident ray and the angle of refraction of the
refracted ray; and calculating the refractive index according to the
formula of law of refraction, also called Snell's law. The
transmission-type method is simple and easy to realize. The measuring
accuracy depends on accurate measurement of the angle of incidence and
the angle of refraction, and the measuring device is complicated.
Meanwhile, the medium to be measured is required to be the optically
transparent medium, such as water, glass, and crystal. The
transmission-type method is not applicable for the turbid medium, such as
milk which is a liquid, because the light passing through the medium will
be scattered and absorbed.

[0006] In the reflection-type method, the refractive index of medium to be
measured is calculated based on the parameters of light reflection
characteristic, such as reflectivity, polarization, phase and critical
angle, wherein the reflection happens at the medium interface. The
critical angle method is typical in the reflection-type method. According
to the law of refraction, when the light passes through the optically
thinner medium from the optically denser medium, the angle of refraction
is larger than the angle of incidence. In addition, when the angle of
incidence increases, the angle of refraction will increase. When the
angle of incidence increases to a certain value, the angle of refraction
will increase to 90 degrees, which means that the refracted ray
propagates along the interface between the two media. The angle of
incidence in this case is called critical angle. If the angle of
incidence continues to increase after achieving the critical angle, the
light will not propagate into the optically thinner medium. Instead, the
light is completely reflected back to the optically denser medium, which
is a phenomenon known as total reflection. When the refractive index of
the optically denser medium does not change, the critical angle only
depends on the refractive index of the optically thinner medium. The
device designed based on this method is called critical angle
refractometer. The measuring method has a simple principle. The measuring
accuracy depends on accurate measurement of the angle. The device is
complicated, but the device is widely applicable for many measuring
objects, comprising non-transparent medium, translucid medium, and
transparent medium, for example, metal, milk, etc.

SUMMARY OF THE PRESENT INVENTION

[0007] In order to solve above problems in conventional technology, the
present invention provides a device for measuring refractive index of
medium based on optical delay technology and its method. An object of the
present invention is to solve a technical problem in conventional methods
for measuring refractive index of medium that angles of light are
required to be measured accurately. However, a measuring system for
measuring the angles of light is complicated, high in cost, and low in
efficiency.

[0008] A principle of the present invention is as follows. In control of
signal processing and controlling module, a first electrical signal is
modulated onto an optical carrier by an optical transmitter module. The
optical transmitter module transmits an optical signal having a certain
wavelength, and the optical signal is injected into a medium to be
measured and propagates therein. The optical signal which is delayed
arrives at an optical receiver module, and then is transformed into a
second electrical signal. The electrical signal is amplified and
transmitted to the signal processing and controlling module. The signal
processing and controlling module measures a delay time between
transmitting the optical signal and receiving the optical signal.
Accordingly, refractive index of the medium to be measured at the certain
wavelength is calculated based on a known length of the medium to be
measured and the delay time. For example, if an optical signal having a
certain wavelength λ0 propagates in a medium, the optical
signal will be delayed by the medium. A delay time is calculated by
Δt=(Ln)/c, wherein Δt refers to the delay time, L refers to a
length of transmission path in the medium, and n refers to refractive
index of the medium at the wavelength λ0, and c refers to
velocity of light in vacuum, which is a constant 300000 km/s. Thus it can
be seen that the refractive index n of the medium at the wavelength
λ0 can be calculated based on the delay time measured
accurately and the known length of the medium L, and n=(cΔt)/L.

[0009] In order to solve the above technical problems, a technical
solution of the present invention is as follows.

[0010] A device for measuring refractive index of medium based on optical
delay technology comprises: a signal processing and controlling module,
an optical transmitter module, and an optical receiver module, wherein
the signal processing and controlling module controls the optical
transmitter module to transmit an optical signal having a certain
wavelength; the optical signal is injected into a medium to be measured;
the optical signal is transmitted in the medium to be measured and
delayed by the medium to be measured; after the optical signal delayed
arrives at the optical receiver module, the optical receiver module
transforms the optical signal delayed into a second electrical signal,
and the second electrical signal is amplified and transmitted to the
signal processing and controlling module by the optical receiver module;
the signal processing and controlling module measures a delay time
between transmitting the optical signal and receiving the optical signal;
the refractive index of the medium to be measured at the certain
wavelength is calculated based on the delay time and a known length of
the medium to be measured.

[0011] The optical transmitter module is preferably a semiconductor laser
or a solid laser, able to transmit an optical signal having a certain
wavelength. After direct intensity modulation or indirect intensity
modulation, the optical transmitter module transmits an optical signal in
a shape of continuous sine or pulse, and injects the optical signal into
the medium to be measured.

[0012] The optical receiver module is preferably a PIN photoelectric
detector or an APD photoelectric detector, which detects the optical
signal transmitted and delayed by the medium to be measured. The optical
receiver module receives the optical signal delayed having a wavelength
matching with the wavelength of the optical signal transmitted by the
optical transmitter module, and transforms the optical signal delayed
into the second electrical signal. The second electrical signal is
amplified, output, and transmitted to the signal processing and
controlling module by the optical receiver module.

[0013] The medium to be measured is a medium through which the optical
signal is able to pass, for example, glass, crystalline material, silica
fiber, plastic fiber, etc.

[0014] The signal processing and controlling module comprises an analog
circuit and a digital circuit, both of which have high accuracy, to
generate a first electrical signal and control to transmit the first
electrical signal. The signal processing and controlling module measures
the delay time between transmitting the optical signal and receiving the
optical signal, according to which the refractive index is calculated.

[0015] The present invention provides a measuring method with a device for
measuring refractive index of medium based on optical delay technology,
which comprises:

[0016] (1) measuring a first delay time of an etalon, i.e., t1, with
the device for measuring refractive index of medium based on optical
delay technology, wherein a refractive index and a length of the etalon
are respectively known as n1 and L1;

[0017] (2) replacing the etalon with a medium to be measured, and
measuring a second delay time t2 with other factors unchanged,
wherein a refractive index and a length of the medium to be measured are
respectively denoted as n2 and L2;

[0018] (3) calculating an additional delay time of an optical signal with
Δt=t1-t2, wherein the additional delay time is caused by
the medium to be measured; and

[0019] (4) calculating the refractive index n2 of the medium to be
measured with a formula, i.e.,
Δt=(n1L1-n2L2)/c, wherein
n2=(n1L1-cΔt)/L2.

[0020] The etalon is a medium having the refractive index and the known
length, wherein the etalon is preferably air or vacuum.

[0021] Compared to conventional technology, beneficial effects of the
present invention are as follows.

[0022] Firstly, optical system is simple and easy to operate. The optical
system transforms measuring of optical parameters into measuring of
optoelectronic signals, in order to decrease complexity of measuring
system.

[0023] Secondly, the device in the present invention is low in cost, and
easy to popularize and apply.

[0024] Thirdly, the measuring method and measuring steps in the present
invention eliminate affection of circuit system, and increase accuracy of
measuring.

[0025] These and other objectives, features, and advantages of the present
invention will become apparent from the following detailed description,
the accompanying drawings, and the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

[0026] FIG. 1 is a sketch view of structure of a device for measuring
refractive index of medium based on optical delay technology according to
a preferred embodiment of the present invention.

[0027] FIG. 2 is a sketch view of the device for measuring refractive
index of medium according to the preferred embodiment of the present
invention, wherein the medium is silica fiber.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0028] Referring to the drawings, the preferred embodiment of the present
invention is further described as follows.

[0029] Referring to FIG. 1, a device for measuring refractive index of
medium based on optical delay technology comprises a signal processing
and controlling module, an optical transmitter module, and an optical
receiver module, wherein the signal processing and controlling module
controls the optical transmitter module to transmit an optical signal
having a certain wavelength; the optical signal is injected into the
medium to be measured; the optical signal is transmitted in the medium to
be measured and delayed by the medium to be measured; after the optical
signal delayed arrives at the optical receiver module, the optical
receiver module transforms the optical signal delayed into a second
electrical signal, and the second electrical signal is amplified and
transmitted to the signal processing and controlling module by the
optical receiver module; the signal processing and controlling module
measures a delay time between transmitting the optical signal and
receiving the optical signal; the refractive index of the medium to be
measured at the certain wavelength is calculated according to the delay
time and a known length of the medium to be measured.

Embodiment

[0030] The optical transmitter module is embodied as a 1.55 μm
semiconductor laser. After direct intensity modulation, the optical
transmitter module transmits an optical pulse signal. The medium to be
measured is embodied as silica fiber. The optical receiver module
comprises a PIN photoelectric detector having a waveband of 1.55 μm, a
pre-amplifier, and a main amplifier; wherein the optical receiver module
detects the optical signal transmitted and delayed by the silica fiber to
be measured, and transforms the optical signal into the second electrical
signal; and the electrical signal is amplified, output, and transmitted
to the signal processing and controlling module by the optical receiver
module. The signal processing and controlling module comprises an analog
circuit and a digital circuit, both of which have high accuracy, to
generate a first electrical signal and control to transmit a first
electrical signal; wherein the signal processing and controlling module
measures the delay time between transmitting the optical signal and
receiving the optical signal; and the refractive index of the silica
fiber at the wavelength of 1.55 μm is calculated according to the
delay time and the known length of the silica fiber to be measured.

[0031] The delay time of the optical signal is accurately measured by
steps of:

[0032] (1) measuring a first delay time of silica fiber, i.e., t1,
with the device for measuring refractive index of medium based on optical
delay technology as shown in FIG. 2, wherein a refractive index and a
length of the silica fiber are respectively known as n1 and L1;

[0033] (2) replacing the silica fiber with a fiber to be measured, and
measuring a second delay time t2 with other factors unchanged,
wherein a refractive index and a length of the fiber to be measured are
respectively denoted as n2 and L2;

[0034] (3) calculating an additional delay time of the optical signal with
Δt=t1-t2, wherein the additional delay time is caused by
the fiber to be measured; and

[0035] (4) calculating the refractive index n2 of the fiber to be
measured with a formula, i.e.,
Δt=(n1L1-n2L2)/c, wherein
n2=(n1L1cΔt)/L2.

[0036] One skilled in the art will understand that the embodiment of the
present invention as shown in the drawings and described above is
exemplary only and not intended to be limiting.

[0037] It will thus be seen that the objects of the present invention have
been fully and effectively accomplished. Its embodiments have been shown
and described for the purposes of illustrating the functional and
structural principles of the present invention and is subject to change
without departure from such principles. Therefore, this invention
includes all modifications encompassed within the spirit and scope of the
following claims.

Patent applications by Qi Qiu, Chengdu CN

Patent applications by University of Electronic Science and Technology of China